Browser automation just got a serious upgrade. Browser Use Terminal v0.1.6 now ships with support for Claude Fable 5, Anthropic's most capable publicly available model and the first of a new capability class the company calls "Mythos." The demo that accompanied the announcement was characteristically unhinged: the agent spent $7.21 autonomously hunting for a coupon code for gum.
A new tier above Opus
Claude Fable 5 is Anthropic's most capable widely released model, built for the most demanding reasoning and long-horizon agentic work. The name change from the familiar Opus/Sonnet/Haiku naming is intentional. Anthropic moved away from the Opus numbering because this model is capable enough to present significant cyber and biological risk without new safeguards. The named class signals a capability tier, not an increment.
The relationship between Fable and Mythos is worth understanding clearly. Mythos 5 is the raw, more capable configuration of the model. Fable 5 is that same model wrapped in production safeguards so it can be offered for general use. Mythos 5 is restricted to Project Glasswing rather than handed out as a normal API model. Think of Fable 5 as the model you can call today, and Mythos 5 as the same engine with the guard rails removed in narrow, controlled settings.
What the numbers look like
The numbers that matter most are the coding and agentic software-engineering evals: 80.3% on SWE-bench Pro, 95.0% on SWE-bench Verified, 29.3% on FrontierCode Diamond, 72.9% on CursorBench 3.1 at max effort, and 88.0% on Terminal-Bench 2.1. Those are strong numbers, particularly on SWE-bench Verified, which tests whether a model can resolve real GitHub issues end-to-end.
The pattern is consistent: the largest gains appear on long, hard, agentic tasks rather than routine chat. That makes the Browser Use Terminal pairing a natural fit. The terminal is exactly the kind of environment where Fable 5's long-horizon reasoning pays off.
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